THE HISTORICAL DEVELOPMENT OF NEUROPHVSIOLOGV 



23 



the excitatory processes (105) in the frog. In his 

 success he had proved his old teacher wrong. In 1844 

 Miiller had said, "The time in which a sensation 

 passes from the exterior of the brain and spinal cord 

 and thence back to the muscle so as to produce a con- 

 traction, is infinitely small and immeasurable." von 

 Helmholtz's technique was as follows: the moment of 

 nerve stimulation, by the break shock of an induction 

 coil, was signalled by the closing of the primary cir- 

 cuit. The resultant muscle contraction lifted a contact 

 in the same circuit, thus breaking it. The break sig- 

 nalled the arrival of the nerve impulse in the muscle. 

 By timing this inter\al, with stimulation at measured 

 distances along the nerve, von Helmholtz was able 

 to calculate its conduction velocity. This simplified 

 description masks the extreme ingenuity of the original 

 experiment. In technique von Helmholtz had coine 

 a long way from Haller's attempt to discover the 

 velocity of nervous action. Haller had read parts of 

 The Aeneid a\oud, timing himself, counting the syllables 

 and calculating the length of the nervous paths used 

 in reading and speaking. In some way that is not 

 entirely clear, he arrived at a figure of 50 m per sec. 



The conduction rate found by Bernstein (approxi- 

 mately 29 m per sec.) tallied sufficiently well with 

 von Helmholtz's final results, 27 to 30 m per sec, for 

 him to be satisfied with the inferred identity of the 

 impulse and the negative variation. Bernstein's experi- 

 ments, using for stimulation a rheotome devised by 

 himself with a galvanometer for detection of response, 

 enabled him to plot the time course of what we now 

 call the nerve's action potential and to determine its 

 latency, rise-time and decay. One of the pregnant ob- 

 servations he made was that the negative variation 

 caused a deflection of his galvanometer that some- 

 times crossed the base line, thus exceeding the value 

 for the resting nerve potential. In today's terminology, 

 he found the overshoot of the action potential beyond 

 the resting potential level. 



Bernstein (106) became widely known for his 

 theory that the membrane of the inactive fiber of 

 nerve or muscle was normally polarized, having po.si- 

 tive ions on the outside and negative ions on the in- 

 side, and that the action potential was a self-propa- 

 gating depolarization of this membrane. This was 



105. VON Helmholtz, H. (1821-1894). Messungen iiber den 

 zcitlichen Verlauf der Zuchung animalischer Muskein 

 und die Fortpflanzungsgeschwindigkeit der Reizung in 

 den Nerven. Arch. Anat. Physiol. 111, 1850. 



106. Bernstein, J. Uber den zeitlichen Verlauf der negativen 

 Schwankung des Nervenstroms. Arch. ges. Physiol, i : 1 73, 

 1868. 



based on his assumption that the membrane is se- 

 lectivelv permeable to potassium ions. His explana- 

 tion of injury currents was that they were the result 

 of a break in the membrane. 



In the later nineteenth century, after a long hiatus, 

 phvsiology in England was again coming into its own. 

 At the half-century, which saw such brilliance in the 

 German schools, there was virtually no physiological 

 work in progress in England. There were no physi- 

 ological laboratories and there was no systematic 

 physiological research. A dual chair in anatomy and 

 physiology had i:)een created in 1836 at University 

 College, London, and had been given to the anatomist 

 William Sharpey. Such teaching as he gave in physi- 

 ology was from books and his pupils saw no experi- 

 ments, yet from among them came the leader of one 

 of the more famous English schools of physiology, 

 Michael Foster (1836-1907), founder of the Cam- 

 bridge School. Though not himself a neurophysi- 

 ologist, Foster could count among his pupils some to 

 become later among the most brilliant in the field, 

 Sherrington (1857-1952), Gaskell (1B47-1914), Lang- 

 ley (1852-1925) and, as descendents from the last, 

 Keith Lucas and in turn Adrian. 



This, the late nineteenth century, was an age of 

 great progress in the development of instrumentation 

 and, with their improved tools, physiologists were able 

 to make more accurate observations of stimulus 

 strength, response characteristics and time relation- 

 ships than had their predecessors. In 1871 Bowditch 

 (107) demonstrated that heart muscle did not respond 

 with graded contractions to graded stimuli. He as- 

 sumed that the global response he observed was due 

 to a leakage of excitation throughout the fiber popu- 

 lation of cardiac muscle. It was in fact the experi- 

 mental evidence for what was later to be called the 

 'all-or-nothing law.' Bowditch, an American, did 

 these experiments in Ludwig's laboratory in Leipzig 

 where he worked on the problem with Kronecker, the 

 teacher of Harvey Cushing. On his return to Harvard, 

 Bowditch founded the first laboratory for physiological 

 research in the United States. 



Forgotten by Bowditch, or unread, were the writ- 

 ings of Fontana in the eighteenth century in which, 

 in discussing heart muscle, he said, "... the irritability 

 of the fibre can be activated by a small cause, and by 

 a feeble impression : but once activated, it has a 

 power proportional to its own forces, which can be 



107. Bowditch, H. P. (1840-191 1). Uber die Eigenthumlich- 

 keiten der Reizbarkeit welche die Muskelfasern des 

 Herzens zeigen. Bcr. Konigl. Sachs. Gesellsch. Wiss. 23: 

 652, 1 87 1. 



